Thank you for the reference to that link. I have read it carefully and am not impressed. Quoting from one of many dubious statements in it:

"Normally, L-tyrosine and L-tryptophan dietary intake provides optimal competitive inhibition balance between dopamine and serotonin precursors with no side effects. However, for proper balance, like force must balance like force. ". The emphases are mine.

The phrase "optimal competitive inhibition balance" sounds very sciencey but it means nothing and "like force must balance like force." sounds like mysticism to me - I doubt that any biomedical scientist (like me) would put much credence on statements like those.

Table 2 in the manuscript covers a very wide (a factor of 200(!)) range of daily tyrosine doses. Nowhere in the manuscript are there any independent clinical accounts of how many patients may have benefited from doses in that very wide range. Until such data are available I don't think that Table 2 says much.

If you want to medicate your father with tyrosine then, in his health interests, please keep well below the Tolerable Upper Limit for it.